# Josh Meyer

### MathWorks

I write MATLAB Math documentation

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**Content Feed**

List of built-in data sets, please

In R2021b, there is now a documentation page with a selection of useful data sets that are in MATLAB: MATLAB Example Data Sets

2 months ago | 3

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Filtration modelisation pdepe derivation problem

Is phi supposed to be a function of x? You currently have phi=linspace(0,0.7,100); and xmesh=linspace(0,0.5e-6,50); So, ...

10 months ago | 0

Can pdepe be used when there is a boundary condition in the centre of the system - Invasion assay

This example shows how to solve a system where there is a material interface: https://www.mathworks.com/help/matlab/math/solve-...

11 months ago | 0

ODE System with 4 equations

When you have a system of equations, each equation gets its own spot in the solution vector y. With the conventions y(1) ...

1 year ago | 0

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How would I manipulate the following functions to use a tall array?

First you need to make a datastore that references the underlying files for each array (one datastore per array). Then you can c...

1 year ago | 0

possibility to add a timeror on ODE15s which after a certain time limit, the solver is stopped or gives a null output

You could implement an event function to do that: https://www.mathworks.com/help/matlab/math/ode-event-location.html Use start...

1 year ago | 0

Solve heat problem by using pdepe

Assuming you want to enforce pr = ur+20; at t=0.03, then you can split the problem into two sub-problems that are solved separat...

1 year ago | 0

Where can I get a samaritan to help me with my code of a Reaction–Diffusion Delayed Neural Networks

You should be able to use pdepe. Just calculate tau in the pdefun function and pass the delayed time value when you call the sub...

2 years ago | 0

Boundary conditions for a ring PDE

pdepe does not allow for time derivatives in the boundary conditions. The boundary conditions are expressed in terms of the flux...

2 years ago | 0

how i can solve the following PDE using periodic boundry coditions

Periodic boundary conditions require that when something leaves one boundary with a certain velocity, it enters the boundary on ...

2 years ago | 0

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PDEPE: How to set I.C as a variable?

pdepe has expectations for the initial condition function. Namely, that it will use the functional signature: function u0 = icf...

2 years ago | 0

Writing PDE boundary conditions

pdepe expects the boundary conditions to be written in a standardized form: Notice that only p can depend on the variable bei...

2 years ago | 0

What is the “pdentrp” function in the “pdepe” function?

This is an internal, private helper function, so it does not have documentation beyond help text. You can access the file with t...

2 years ago | 1

Retaining the max value during scattered data interpolation

You'll need to do this manually before calling scatteredInterpolant. There are a few ways to do it, you could use a logical mask...

2 years ago | 0

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PCG and MINRES question

Since A*x = b, the sizes of the variables must be: A * x = b (M-by-N) * (N-by-1) = (M-by-1) But since alm...

2 years ago | 0

Getting the intermediate solutions in an iterative solver

While the functions themselves don't return intermediate results, consider that the resvec output of all the iterative solvers r...

2 years ago | 0

why convergence is not happening in pcg function ?

There are two things to notice here: In the first message you printed where PCG converges after 1 iteration, this is an indicat...

2 years ago | 0

PCG on a large sparse matrix from Finite difference method

Yes, you can provide the coefficient matrix as a function handle instead of a numeric matrix. This is because PCG, like many of ...

2 years ago | 0

Best integration method to integrate this oscilating function

integral can handle oscillatory integrands as long as there aren't too many oscillations, and you supply plenty of WayPoints in ...

2 years ago | 0

Processing Data in a Tall Array

findgroups and splitapply work with tall arrays, so don't worry about using tall.transform or tall.reduce for this simple task. ...

2 years ago | 0

How does integral2 work?

The basic principle of numeric integration is you are calculating the area under the curve by splitting it up into smaller piece...

2 years ago | 0

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Problem with boundary conditions for PDEPE

From the doc for pdepe, "When m > 0 and a = 0, boundedness of the solution near x = 0 requires that the flux f vanish at a = 0....

2 years ago | 0

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what's the difference in accuracy between solving a stiff problem by ode15s and ode45?

Stiffness is more of an issue of stability than accuracy. Nonstiff solvers can solve stiff problems, it just takes them a long t...

2 years ago | 1

Change font size of node name in a graph

Several new properties were added to GraphPlot objects in R2018b to enable customization of node and edge labels. In particular ...

2 years ago | 3

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Problems with pdepe with disconnected variables in c, f and s

c, f, and s are expected to be column vectors with length equal to the number of equations being solved. Since you have 1 equati...

2 years ago | 1

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Implementing boundary condition in pdepe

The form for the boundary conditions expected by the solver is Since you have a system of two equations, each p and q should ...

3 years ago | 0

pdepe help! (boundry condition in PDE solver)

Your boundary condition function includes the line pl = ul-TT(i); TT(i) is not defined within view of the function, so that i...

3 years ago | 2

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'Undefined Function or Variable' Error when Function is Defined

Looks like the issue is you define cp in the workspace and the function can't access that variable when it gets called. So, try ...

4 years ago | 0

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Use griddata ignoring gaps in data

To interpolate without the gaps you need to remove them from the data before interpolating, request values on the full grid (inc...

4 years ago | 1

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system of 1st and 2nd order differential equations ode45

The documentation explains how to express higher-order equations as first-order equations: <https://www.mathworks.com/help/matl...

4 years ago | 0